This invention relates to circuit breakers, and, more particularly, to a rotary contact assembly for high ampere-rated circuit breakers.
U.S. Pat. No. 4,616,198 entitled Contact Arrangement For A Current Limiting Circuit Breaker, describes the early use of a first and second pair of circuit breaker contacts arranged in series to substantially reduce the amount of current let-through upon the occurrence of an overcurrent condition. A more recent description is found within U.S. Pat. No. 6,114,641 entitled Rotary Contact Assembly For High Ampere-Rated Circuit Breakers.
When the contact pairs are arranged upon one movable contact arm such as described within U.S. Pat. No. 4,910,485 entitled Multiple Circuit Breaker With Double Break Rotary Contact, some means must be provided to insure that the opposing contact pairs provide a wiping action upon closure to remove any oxides or other contaminants developed upon the contact surfaces.
One arrangement for providing such wiping motion within circuit breakers containing pivotally-arranged contacts is within U.S. Pat. No. 5,361,051 entitled Pivoting Circuit Breaker Arm Assembly. This arrangement includes an elongate slot formed within the moveable contact arm to provide wiping action upon contact closure. Early teachings of the use of a slotted moveable contact arm for wiping the circuit breaker contacts is found within U.S. Pat. No. 4,756,628 entitled Circuit Breaker, as well as U.S. Pat. No. 4,484,164 entitled Braidless Movable Contact With Wiping Action.
In so-called xe2x80x9cvacuumxe2x80x9d circuit interrupters, wherein continuous wiping of the contact surfaces is imperative to long term operation, the wiping motion is achieved by the addition of a wiping spring in addition to the contact closing springs for continued motion of the contacts in the parallel plane after the closing springs have initially become engaged. One example of a wiping spring used within vacuum circuit breakers is found in Canadian Patent No. CA 1,098,570 entitled Contact Controller For Vacuum-Type Circuit Interrupter.
It would be economically advantageous to provide rotary contacts with wiping action upon contact closure without having to employ elongated pivot openings within the contact arms and without having to employ an auxiliary wiping spring.
In an exemplary embodiment of the invention, automatic contact wiping between circuit breaker rotary contacts upon contact closure is provided for removing contaminants and oxides from the contact surfaces, at a minimum increase in manufacturing costs. The circuit breaker rotary contact assembly employs a common pivot between the rotor assembly and the rotary contact arm. A pair of off-center expansion springs directly engage the rotor at one end and engage the rotary contact arm via a linkage arrangement at an opposite end thereof. Separate pivots are provided to the rotor assembly and the moveable contact arms ensure that the contacts close prior to complete rotation of the rotor assembly. The additional rotation force provided by the rotor assembly then translates into lateral displacement of the moveable contacts relative to the fixed contacts, resulting in contact wiping function.
An alternate embodiment utilizes a common pivot point between the rotor assembly and the moveable contact arms, while providing slight post closure motion by means of a fixed contact support spring.